power: qpnp-vm-bms: improve wake-up source handling

VM-BMS driver holds a wake-up source while charger is in
Constant Voltage(CV) state and the check for conditions to
hold/release wake-up source is done in the monitor_soc_work.
In situation when USB is removed in the CV state the wake-up
source can only be released once monitor_soc_work is scheduled.

Fix this by scheduling monitor_soc_work for every power_supply
change event.

CRs-Fixed: 808127
Change-Id: I2d93292557f293b2931acc32876b637de9f02d19
Signed-off-by: Ashay Jaiswal <ashayj@codeaurora.org>